1. Field of the Invention
This invention relates to a method for regulating a fan in a compressor unit which comprises at least one compressor element, at least one motor with electronically adjustable speed driving this compressor element, and at least one cooler comprising at least one radiator and at least one fan cooperating therewith, driven by an electric motor, whereby the motor of the compressor element is driven at a speed varying in function of its load.
2. Discussion of the Related Art
In an air-cooled air compressor with oil lubrication, such cooler can be provided in the outlet of the compressor element, before or after the oil separator or the pressure vessel.
In this application, oil must be comprehended in a broad sense. By oil, not only mineral oil must be understood, but also any viscous agent which can be used for lubricating and cooling rotors, gear wheels or bearings and which is hydrophobic or incompatible with water.
In a multistage-compressor, the cooler can be mounted in between the stages.
In the known compressor units, the fan, during cooling, always is driven at a constant number of revolutions, to wit a number of revolutions whereby it still can cool sufficiently in the worst working circumstances of the compressor element, this is with the highest working pressure, at maximum load, and with the highest air humidity and air temperature.
In consideration of the fact that the load of the motor of the compressor element and, therefore, also its number of revolutions, varies, a constant speed of the fan at a low load results in too large a cooling.
In the first place, this is disadvantageous for the energy consumption. If the fan motor at its set number of revolutions consumes, for example, 5 kW of power, this will be only 0.2 kW with the minimum number of revolutions.
In the second place, this constant number of revolutions brings along that the cooling may be too large, which can result in a condensation of moisture originating from the suctioned and compressed air.
If the compressor is a compressor cooled by means of oil, then the condensed water in the oil is strongly disadvantageous for the working of the compressor element.
If the same oil also is used for lubricating the bearings, then the water in the oil is very bad for the service life of this latter.
In such oil-cooled compressor, the oil, after the compressor element, is separated in an oil separator and returned to the compressor element.
It is known to place the cooler into the return conduit for the oil and to place a thermostatic valve in this return conduit, which valve, when the temperature of the oil drops below a certain border value, redirects the oil to the compressor element via a bypass of the cooler.
The oil which is injected into the compressor element therefore does not cool off further, as a result of which the compressed air getting into the oil separator can be sufficiently warm, as no moisture should condensate there.
As the fan further revolves at full speed, whereas the oil is flowing through the bypass, this fan further cools down the radiator. When then the oil is sufficiently warm because the thermostatic valve again shall alter its position, warm oil gets into this radiator, which brings along large thermic shocks.
The further revolving fan also cools down other parts of the compressor, such that, even if the oil is not directed through the cooler, this can be cooled somewhat and the formation of condensation in the oil separator still is not excluded.
In multistage-compressor units, an intermediate cooler cooled by a fan driven at a constant number of revolutions at low load also may cool too much, which also may lead to the formation of condensation.
Even in the case of an oil-free multistage-compressor unit, water drops which, with the air at high speed, are carried along in the high-pressure stage, may cause damages there.
The invention aims at a method for controlling a fan in a compressor unit which remedies said disadvantages and, in the first place, allows to avoid condensation problems and further has a better energetic efficiency, reduces or prevents thermic tensions in the coolers and can reduce the noise level.
According to the invention, this aim is achieved in that the number of revolutions of the motor of the fan is regulated in function of the required cooling, however, such that condensation of moisture due to exaggerated cooling is avoided.
U.S. Pat. No. 5,910,161 describes a method whereby the motor of fans of a compressor unit is regulated, however, the compressor unit forms part of a cooling device, and the fans cool the condensers in the cooling circuit, and this such that in these condensers, the cooling medium is condensed completely.
Also U.S. Pat. No. 5,873,257 relates to a cooling device whereby also the condenser is cooled by a fan of which the speed of the motor is regulated in this manner. Of course, in the condenser a condensation of the cooling medium is taking place. Also opposite to the evaporator, a fan with controlled motor is installed, however, this evaporator is no cooler.
According to the invention, preferably the speed of the motor of the fan is regulated in function of the speed of the motor of the compressor element.
The speed of the motor of the fan can be regulated in function of the speed of the motor driving the compressor element, such that the ratio of the speeds of both motors takes a course according to an empirically determined curve.
The invention also relates to a compressor installation with a fan which is regulated according to the method according to the invention, described in the aforegoing.
Thus, the invention relates to a compressor unit comprising at least one compressor element, at least one motor with electronically adjustable speed which drives this compressor element at a speed varying in function of its load, and at least one cooler which comprises at least one radiator and at least one fan cooperating therewith, driven by an electric motor, whereby the characterizing feature consists in that the motor of the fan is a motor with electronically adjustable speed and is coupled to means for regulating its speed in function of the required cooling, such that its speed varies in function of the required cooling, whereas condensation of moisture due to exaggerated cooling is avoided.
The speed regulating device or otherwise means for regulating the speed of the motor of the fan preferably are coupled to the seed regulating device or otherwise means for regulating the speed of the motor driving a compressor element.
Thereby, the means for regulating the speed of the motor of the fan can be coupled such to the means for regulating the speed of the motor driving a compressor element that the ratio of the speeds of both motors takes a course according to an empirically determined curve.
In a practical embodiment, the compressor unit comprises an oil-cooled compressor element to which a pressure conduit connects in which an oil separator is mounted, whereby this oil separator is connected to the compressor element by means of a return conduit for oil in which the radiator of an oil cooler with a fan is mounted and this fan is the fan which is coupled to said means for regulating its speed.
In another embodiment, the compressor unit comprises several stages and thus at least a low-pressure compressor element and a high-pressure compressor element and, in the intermediate conduit connecting the two compressor elements to each other, the radiator of an intermediate cooler with a fan is mounted and is this fan the fan which is coupled to said means for regulating its speed.